A paging system is a one-way (wireline to mobile) digital transmission system. Message paging systems will grow with evolution of electronic-mail services, wherein the message communication hardly interrupts the person being called.
A mobile station (MS) of a mobile communication system has three states, i.e. idle, standby, and active. Data can be transmitted between the mobile station and the mobile communication network only when the mobile station is in the active state. In the active state, the cell location of the mobile station is known to the mobile communication network.
Looking at the MS-UTRAN level, an MS basically has only two service states (in the following referred to as UTRAN service states) seen from the higher layer perspective, namely idle and RRC connected. The RRC connected state has further substates that are not visible to the higher layers and/or core network entities. These substates are based on the current channel allocation situation and are called Dedicated Channel (DCH) Active state and Common Channel state. The MS is moved between these two states (and within the substates of these two states, explained below) based on the data activity level of the MS.
The DCH Active state is further divided into two substates based on the type of radio bearer to which a dedicated channel is currently allocated and are called User Data Active state and Control Only state.
The Common Channel state is further divided into two substates based on the accuracy at which an MS location is known in the UTRAN, which is also directly related to the type of downlink common channel which can be used to communicate to the MS. These substates are called RACH/FACH state and RACH/PCH state.
The RACH/PCH state is further divided into two substates based on the accuracy at which the MS location is known within this state. These states are called Single Cell PCH state and URA (UTRAN Registration Area) state.
In the idle state, the MS does not have a logical network context activated or any corresponding addresses allocated. In this state, the MS can only receive multi cast messages which can be received by any MS. Since the mobile communication network does not know the location of the MS, it is not possible to send messages to the MS from external networks.
If multiple non-coordinated core networks are connected to one radio access network (such as UTRAN) of the mobile communication network and one of the core networks has an active connection with an MS, while a “non-active” core network starts paging towards the MS, a special procedure is required to transfer the paging message to the mobile station, because the MS normally does not listen to a paging channel during the active state.
In a GSM-GPRS system, only class-A mobile stations (capable of simultaneously listening both GSM and GPRS control channels) can be paged, if a Gs interface between a Mobile Switching Center (MSC) and an SGSN (Serving GPRS Support Node) is missing. If the Gs interface exists and the MS is attached to the GPRS, it can be paged from the circuit-switched side (GSM) using GPRS channels. If a GPRS data channel is active, the circuit-switched paging can be routed via that data channel.
However, no solution has been proposed so far as to a paging control method to be performed if a circuit-switched call is active and a paging request arrives from a non-coordinated packet-switched network.
Also, for the UMTS system, where only one set of control channels in UTRAN are available even if two independent core network entities are connected to the same UTRAN, a novel method is required for the paging control.